Many  of the victims, of whom 83 were children, were burned to death in their homes, while others were hacked to death with machetes in 75 separate massacres, the UN Joint Human Rights Office (UNJHRO) said in a press statement following the report's release on Wednesday.

“Investigators found that the victims were often those least able to flee the attacks, largely children and the elderly,” the UNJHRO added.

The actual number of those killed "could be considerably greater," the organization said, as security restraints had prevented assessors from being able to confirm "many more" reports of human rights violations.

It said the figures referred to cases documented in only some parts of Masisi over a relatively limited period of time, and were therefore far from presenting a comprehensive overview of the human rights situation throughout eastern DRC.

'Angry villagers'

The report revealed that six UN investigations had determined that the Raja Mutomboki and Nyatura armed groups were responsible for the majority of the mass killings. Raïa Mutomboki, which means "angry villagers" in Kiswahili, is an armed group from the South Kivu province.

The group formed in 2008 to defend local residents against the Democratic Forces for the Liberation of Rwanda (FDLR), a Hutu militia group made up of former participants in the Rwandan genocide in 1994 who subsequently  fled to the Democratic Republic of Congo. One reason for the increase in violence, the report explained, is the groups' desire to take advantage of the weak security situation in the eastern DRC.

UN experts have openly criticized Uganda for actively supporting rebel groups. Uganda has denied these allegations and immediately shut down a border post with the DRC in order to prevent a Congolese rebel group from accessing a source of revenue.

In a statement, the Ugandan government said it was concerned that M23 rebels were taking advantage of the border crossing "to collect revenue from cargo vehicles and other goods."

The M23 insurgency began in April when DRC army officers defected, launching a rebellion to demand better pay, arms and an amnesty for war crimes charges.

M23 is believed to be led by former Congolese general Bosco Ntaganda, who is wanted by the International Criminal Court to face allegations of carrying out war crimes.

Ceasefire over

Meanwhile, a two month ceasefire in the eastern Democratic Republic of Congo has been broken amid reports fighting between government forces and rebels has resumed.      

Late on Thursday, M23 said it had been attacked by government troops and were forced to retaliate. Government officials, meanwhile, blame the rebels for initiating the latest outbreak of violence, saying dozens died unnecessarily in the attack.

 Over the past few days, as the conflict in the DRC escalated, thousands of refugees have fled the central African country and have headed to Rwanda, adding to the hundreds of thousands already displaced by the conflict.

DRC Army Colonel Olivier Hamuli told the AP news agency that fighting broke out in Rugari, a town situated between the rebel forces and government troop defence lines, about 30 kilometers (19 miles) from Goma, the provincial capital.

Earlier in the week, international observers in the country had warned that rebel forces appeared to have positioned themselves for what seemed like an imminent attack.

Members of the International Conference for the Great Lakes Region have been in talks since mid-August in Kampala, Uganda, in a bid to find a solution to the conflict, but still tensions have continued to rise over the past two weeks.